The present invention relates generally to light modulators, and more particularly, to light modulators capable of generating microwave-frequency light signals.
Present techniques for producing modulation of light generally make use of a controlled variation in the electrical signal energy supplied to the light source, or make use of electrooptic or acoustooptic interactions with light from a continuously emitting source. The maximum modulation frequency presently obtainable with these methods is a few gigahertz at best, and such modulation rates in the gigahertz range require significant driving circuits and microwave packaging. Thus, the cost size, electrical power dissipation, and complexity increase rapidly for modulation frequencies above approximately 100 MHz. By way of example, it is estimated that a source of modulated light with a 1 GHz bandwidth using state-of-the-art technology would cost more than $10,000, require an electrical drive power in excess of 10 watts, and contain dozens of electronic and optoelectronic components. It has been suggested to interfere or beat the light from two lasers to produce high frequency intensity modulation at the difference frequency. However, it is difficult to stablize the laser frequencies to a degree adequate to insure high spectral purity and low FM noise in the beat signal. In this regard, see the article "Optical FSK Heterodyne Detection Experiments Using Semi-Conductor Laser Transmitter and Local Oscillation", by S. Saito, Y. Yamamoto, and T. Kimura, IEEE J. Quantum Electronics, 1981, QE-17, pages 935-941.